WO2006070749A1

WO2006070749A1 - METHOD FOR PRODUCING SILICON CARBIDE (SiC) SINGLE CRYSTAL AND SILICON CARBIDE (SiC) SINGLE CRYSTAL OBTAINED BY SUCH METHOD

Info

Publication number: WO2006070749A1
Application number: PCT/JP2005/023798
Authority: WO
Inventors: Yasuo Kitaoka; Takatomo Sasaki; Yusuke Mori; Fumio Kawamura; Minoru Kawahara
Original assignee: Matsushita Electric Industrial Co., Ltd.; Osaka University
Priority date: 2004-12-28
Filing date: 2005-12-26
Publication date: 2006-07-06
Also published as: EP1739211A4; CN1922346A; JPWO2006070749A1; KR100806999B1; KR20070069089A; JP5049590B2; US7419545B2; CN100567596C; EP1739211A1; US20070221122A1

Abstract

Disclosed is a method for producing a large-sized silicon carbide (SiC) single crystal at low cost. Specifically, a silicon carbide single crystal is produced or grown by melting and reacting silicon (Si) and carbon (C) in an alkali metal flux. Lithium (Li) is preferable as the alkali metal. By this method, a silicon carbide single crystal can be produced under low temperature conditions, for example, at 1500˚C or less. One example of the silicon carbide single crystal obtained by this method is shown in the photograph of Fig. 3(B).

Description

Specification

Method for producing silicon carbide (SiC) single crystal and silicon carbide (Si C) single crystal obtained thereby

Technical field

The present invention relates to a method for producing a silicon carbide (SiC) single crystal and a silicon carbide (SiC) single crystal obtained thereby.

Background art

[0002] Silicon carbide (SiC) single crystal is a promising semiconductor material having a wide band gap, high thermal conductivity, high insulation electric field, and large saturation electron velocity. Because of these characteristics, semiconductor devices manufactured using silicon carbide single crystal force can be operated at high operating temperatures, high speeds, and high output levels. For example, automotive power devices are energy devices. It is a promising semiconductor device.

As conventional silicon carbide single crystal growth methods, the sublimation method, the Atchison method, liquid phase growth, and the like are known. The sublimation method is a method in which SiC is used as a raw material, and this is heated and sublimated to precipitate a single crystal in a low temperature part. The Atchison method is a method in which carbon and silica are reacted at a high temperature. Liquid phase growth is a method in which a silicon compound is dissolved in a carbon crucible and carbon and silicon are reacted at a high temperature to precipitate a single crystal. However, the conventional growth methods have various problems as shown below. First, a common problem in these methods is that a high temperature is required for crystal growth. In addition, in the sublimation method, the obtained single crystal has many micropipes, stacking faults, and the like, so there is a problem in the quality of the obtained crystal. In other words, it is difficult to control the partial pressure of these gases to the stoichiometric composition because the raw materials are vaporized as Si, SiC, and Si C during sublimation. Is considered to be formed. In liquid phase growth, it is difficult to grow large crystals because the amount of carbon dissolved in the silicon solution is small.

[0004] In recent years, in order to solve the above-mentioned problems, in the liquid phase growth method, Si, C and transition metals are melted to form a melt, and a seed crystal is brought into contact with the melt to produce a SiC single crystal. Have been reported (see, for example, Patent Documents 1, 2 and 3). In this method, the graphite crucible is A raw material having a composition of Ti was inserted, and the crucible was heated to 1850 ° C in an Ar atmosphere at atmospheric pressure to dissolve the raw material, and then at 1850 ° C so that graphite was dissolved in the melt. Hold for 5 hours. Thereafter, the 6H—SiC seed crystal is immersed in the melt, cooled to 1650 ° C. at a rate of 0.5 ° C./min, and grown. It has been reported that a SiC crystal having a thickness of 73 2 zm was formed by this method. However, this method also has a problem that high temperature is required for crystal growth. In other words, the melting point of Si is 1414 ° C, the melting point of C is 3500 ° C, the melting point of Ti is 1675 ° C, and the melting point of SiC is 2545 ° C, so a high temperature condition of at least 1700 ° C is required. Become. In particular, when transition metals such as Ti are used, crystal growth at low temperatures is difficult because of their high melting points. As another method, a method of producing 3C_SiC single crystal by crystal growth using SiC as a raw material in a liquid phase growth method has been reported (Patent Document 4). To obtain crystals, high temperature treatment is required. On the other hand, it is generally said that in order to produce a high-quality SiC single crystal substrate at a low cost, it is necessary to produce the single crystal under a low temperature condition of 1500 ° C or lower.

Patent Document 1: JP 2000-264790 A

Patent Document 2: JP 2002-356397

Patent Document 3: Japanese Patent Laid-Open No. 2004-2173

Patent Document 4: U.S. Pat.No. 4,349,407

Disclosure of the invention

Problems to be solved by the invention

Accordingly, an object of the present invention is to provide a method for producing a silicon carbide single crystal capable of producing a large silicon carbide (SiC) single crystal at low cost.

Means for solving the problem

[0006] In order to achieve the above object, the production method of the present invention involves dissolving silicon (Si) and carbon (C) in an alkali metal flux and reacting them to form a silicon carbide unit. This is a manufacturing method for generating or growing crystals.

[0007] The silicon carbide single crystal of the present invention is a silicon carbide single crystal obtained by the production method of the present invention. The invention's effect

As described above, in the production method of the present invention, silicon and carbon are dissolved in an alkali metal flux and reacted with each other. For example, the temperature condition is low (eg, 1500 ° C. or lower). However, it is possible to produce a silicon carbide single crystal. For this reason, according to the manufacturing method of the present invention, a large silicon carbide single crystal can be manufactured at low cost.

Brief Description of Drawings

[0009] [Fig. 1] Fig. 1 (A) is a schematic diagram showing an example of a production apparatus used in the production method of the present invention, and Fig. 1 (B) shows a pressure-resistant and heat-resistant container in the production apparatus. It is an enlarged perspective view

FIG. 2 is a photograph of an aggregate of SiC single crystals obtained in one example of the production method of the present invention.

FIG. 3 (A) and (B) are enlarged photographs of the SiC single crystal.

FIG. 4 is a chart showing the results of X-ray diffraction evaluation of the products in the crucible in the example.

FIG. 5 (A) is a schematic diagram showing a method of X-ray diffraction, and FIG. 5 (B) is a chart showing the results of X-ray diffraction evaluation of the SiC single crystal.

FIG. 6 is another chart showing the X-ray diffraction evaluation results of the SiC single crystal.

FIG. 7 is a chart showing the results of X-ray diffraction evaluation of products obtained in other examples of the present invention.

Explanation of symbols

[0010] 11 Gas tank

12 Pressure regulator

13 Electric furnace

14 Pressure and heat resistant container

15 crucible

16 Leak valve

BEST MODE FOR CARRYING OUT THE INVENTION [0011] In the production method of the present invention, it is preferable that the silicon carbide single crystal is generated or grown by cooling the alkali metal flux in which the silicon and the carbon are dissolved. That is, for example, by heating the silicon, the carbon, and the alkali metal, the silicon and the carbon are dissolved in the alkali metal flux, and the heating state is maintained for a certain time, and then the heating temperature is decreased. It is preferable to cool the alkali metal flux. Hereinafter, this method is referred to as “temperature drop method”. In the temperature drop method, the initial temperature of the heat treatment (growth initial temperature), the final temperature after the drop, the temperature drop rate, etc. are not particularly limited and can be determined as appropriate.

[0012] In the manufacturing method of the present invention, a temperature gradient is formed in the alkali metal flux, the silicon and the carbon are dissolved in a high temperature region of the temperature gradient, and the low temperature region of the temperature gradient is It is preferable to produce or grow a silicon carbide single crystal. Hereinafter, this method is referred to as “temperature gradient method”. In the temperature gradient method, the temperature in the high temperature region and the low temperature region is not particularly limited and can be determined as appropriate.

[0013] In the production method of the present invention, the alkali metal flux force includes lithium (Li). S is preferable, and a flux of lithium alone is particularly preferable. The present invention is not limited to this, and the flux is, for example, other alkali metals such as sodium (Na) and potassium (K), and alkaline earth metals (for example, calcium (Ca)). It contains other elements such as

[0014] In the production method of the present invention, the generation or growth of the single crystal is preferably performed in a heated atmosphere. The heating temperature is, for example, not more than 1500 ° C, preferably in the range of 200 to 1500 ^o C, more preferably in the range from 400 to 1500 ^o C, more preferably in the range of 600 to 1400 ° C is there. The heating temperature can be determined as appropriate depending on, for example, the composition of the flux. Among these, the heating temperature is preferably not more than the boiling point of the element that is the main component of the flux, because the evaporation of the flux component can be further suppressed.

[0015] In the production method of the present invention, as described later, it is preferable that the generation and growth of the single crystal be performed in a pressurized atmosphere, for example, in the range of 0.1 to:! OOMPa. Yes, preferably in the range of 0.:! To lOMPa, more preferably in the range of 0.:! To IMPa. In addition, the generation or growth of the single crystal is preferably performed in an inert gas atmosphere. Said Examples of the inert gas include argon (Ar) gas and hydrocarbon gas such as methane and propane, and more preferably argon gas.

[0016] In the production method of the present invention, the proportions of alkali metal, silicon and carbon as flux components are not particularly limited. For example, when lithium is used alone as a flux component, the ratio (mol ratio) of Li, Si, and C is, for example, Li: Si: C = l: (0. 01 to: 10 0): (0. 01 ~: 100), preferably Li: Si: C = l: (0. 01 ~: 10): (0. 01 ~: 10), more preferably Li: Si: C = l: (0 01 ~: 1): (0. 01 ~: 1).

[0017] In the production method of the present invention, it is preferable that the reaction is performed in a reaction vessel, and the carbon is supplied with the material component force of the reaction vessel.

In the production method of the present invention, it is preferable that a silicon carbide crystal prepared in advance is used as a seed crystal, and a new silicon carbide single crystal is grown using the seed crystal as a nucleus. The seed crystal is preferably in the form of a substrate. In this case, for example, a silicon carbide crystal may be formed in a thin film on the surface of a substrate made of another material. As the silicon carbide crystal used as the seed crystal, for example, 6H-SiC crystal and 4H-SiC crystal are preferable. In the manufacturing method of the present invention, a 2H-SiC single crystal is manufactured on a 6H-SiC crystal substrate. It is preferable to do. Further, as the seed crystal, a commercially available silicon carbide crystal or a carbide crystal substrate can be used.

Examples of the silicon carbide single crystal obtained by the production method of the present invention include 6H—SiC single crystal, 4H—SiC single crystal, 3C—SiC single crystal, and 2H—SiC single crystal. Of these, 2H—SiC single crystals are particularly preferred because of their high practicality because they have the largest band gap and high electron mobility. In the present invention, for example, a 2H—SiC single crystal means a material that can be used practically as a 2H—SiC single crystal, and is not limited to one that is formed strictly from 2H—SiC. The same applies to 3C_SiC single crystals and other single crystals.

In addition, the manufacturing method of the present invention can be used for manufacturing semiconductor devices, for example. That is, in the method for manufacturing a semiconductor device, for example, by forming a silicon carbide single crystal on a substrate using the manufacturing method of the present invention, a semiconductor device including a silicon carbide single crystal layer can be manufactured at low cost. Examples of the substrate include a 6H_SiC crystal substrate and a 4H_SiC crystal substrate, and the silicon carbide single crystal includes, for example, a 2H_SiC single crystal. preferable.

Next, the silicon carbide single crystal of the present invention is a silicon carbide single crystal obtained by the production method of the present invention. This silicon carbide single crystal is of higher quality than that produced by conventional methods.

Next, the production method of the present invention will be described with examples.

FIGS. 1A and 1B show an example of an apparatus used in the production method of the present invention. As shown in FIG. 1 (A), this apparatus includes a gas tank 11, a pressure regulator 12, an electric furnace 14, and a pressure and heat resistant container 13. A pressure-resistant and heat-resistant container 13 is arranged in the electric furnace 14, and a crucible 15 is arranged in the pressure-resistant and heat-resistant container 13 (FIG. 1 (B)). In the crucible 15, flux components and raw materials silicon and carbon are arranged. The gas tank 11 is connected to the pressure-resistant and heat-resistant container 13 by a pipe, and a pressure regulator 12 is disposed in the middle thereof. The gas tank 11 is filled with an inert gas such as argon (Ar), for example. The pressure of the gas can be adjusted to, for example, 1 to: 100 atm (0.1 to: OMPa) from the pressure regulator 12 and supplied into the pressure and heat resistant container 13. By adjusting the atmospheric pressure to a pressurized condition, evaporation of the flux component (eg, lithium) can be suppressed. In the figure, 16 is a leak valve. Examples of the electric furnace 14 include a resistance heater and the like, and a resistance heater and a heat insulating material force may be configured. When the heating element in the resistance heater is heated to 1500 ° C, for example, MoSi or the like can be used. On the other hand, when used at 1000 ° C or less, for example, a Kanthal wire can be used. Is extremely easy. As the pressure resistant and heat resistant container 13, for example, a stainless steel container or the like is used and heated in the electric furnace 14. In addition, the container disposed in the electric furnace 14 is not limited to a pressure and heat resistant container. For example, by adjusting the difference between the pressure in the electric furnace and the pressure in the container disposed in the electric furnace, Containers can be used. As a material of the crucible 15, for example, a material resistant to lithium metal such as tungsten (W) or SUS can be used. As the crucible 15, for example, a crucible formed from a carbon-based material such as a graphite crucible may be used, or a material force resistant to lithium metal may be used. System material force A crucible formed may be arranged. Thus, when a crucible formed from a carbon-based material is used, carbon as a crystal raw material can be supplied with a crucible material force. In the present invention, In addition to silicon or the like, other components may be placed in the crucible 15. For example, doping impurities may be added. Examples of the P-type doping material include A1 and B. Examples of the N-type doping material include N and P.

The production of a SiC single crystal using this apparatus can be performed, for example, as follows. First, in a glove box, lithium, silicon, and carbon are weighed and put in a crucible 15, and this crucible 15 is set in a pressure and heat resistant container 13. Then, argon gas is supplied from the gas tank 11 into the pressure and heat resistant container 13. At this time, the pressure is adjusted to a predetermined pressure by the pressure regulator 12. Then, the inside of the pressure and heat resistant container 13 is heated by the electric furnace 14. Then, since the boiling point of lithium is 1327 ° C. in the crucible 15, lithium is first dissolved to form a flux (melt), in which silicon and carbon are dissolved. The heating temperature is, for example, 1500 ° C. or less, preferably the boiling point of the lithium, more preferably 1000 ° C. or less, and further preferably 950 ° C. or less, 850 ° C. or less. For example, the melt temperature can be further increased by increasing the atmospheric pressure, which can further improve the solubility of silicon and carbon. The atmospheric pressure is as described above. As the atmospheric gas, for example, a hydrocarbon gas such as methane or propane can be used in addition to the argon gas. When the temperature drop method as described above is adopted, for example, the temperature of the melt is kept constant, silicon and carbon are sufficiently dissolved, and then the melt temperature is lowered to reduce the temperature of the SiC unit. Crystals can be generated or grown. The holding temperature of the melt is, for example, 200-1500. C, preferably 1000. C or lower, more preferably 950 ° C or lower and 850 ° C or lower. The temperature drop rate (temperature drop rate) is preferably in the range of, for example, 0.1 to 100 ° C./h, where a constant rate is preferred. In addition, as in the above-described temperature gradient method, it is possible to form a temperature gradient in the flux and simultaneously dissolve the crystal raw material and generate or grow a single crystal. This temperature gradient method is, for example, a method in which, in the flux, two regions having different temperatures, a temperature region where a crystal raw material is dissolved (high temperature region) and a temperature region where a single crystal is generated or grown (low temperature region) are provided. is there. The temperature difference between the high temperature region and the low temperature region is preferably in the range of 10 to 500 ° C., for example. Moreover, when using a seed crystal, it is preferable to make this seed crystal and its periphery into a low temperature area | region. A method of forming a temperature gradient in the flux. For example, there are the following methods. That is, first, silicon and carbon as raw materials are filled at the bottom of a crucible containing flux (melt), and silicon carbide as a seed crystal is fixed at the top of the crucible. The heater is divided into two zones, and a difference is formed between the temperature of the crucible bottom, which is the raw material part, and the growth part where the seed crystal is fixed. By setting the crucible bottom to a high temperature and the growth to a low temperature, silicon and carbon dissolve in the flux (melt) and react to grow a single crystal on the seed crystal in the low temperature. .

When a 2H—SiC single crystal is manufactured by the manufacturing method of the present invention, the heating temperature of the growth region is set to 600 ° C. C force is preferred, more preferably ί or 700-850. C. When growing a single crystal by the temperature drop method, the initial growth temperature is preferably 750 to 850 ° C, more preferably 800 to 850 ° C. For example, it is preferable to hold at this initial temperature for 1 to 100 hours, more preferably 10 to 50 hours. Then, the temperature is gradually lowered from the initial temperature to grow a single crystal, and the final temperature is preferably set to 600 to 800 ° C, for example, more preferably 700 to 800 ° C. When growing a single crystal by the temperature gradient method, the high temperature region is preferably, for example, 800 ° C or more, more preferably 850 ° C or more, and the low temperature region is, for example, 600 to 850 ° C. Force S is preferable, more preferably 700 to 850 ° C. Further, when a 3C—SiC single crystal is produced by the production method of the present invention, the heating temperature of the growth region is preferably 850 to 1000 ° C., more preferably 850 to 950 ° C., for example. When the single crystal is grown by the temperature drop method, the initial growth temperature is preferably 900 to 1000 ° C. force S, for example. At this initial temperature, for example, it is preferable to hold for 1 to 100 hours, more preferably 10 to 50 hours. Then, the temperature is gradually lowered from the initial temperature to grow a single crystal, and the final temperature is preferably set to 850 to 950 ° C., for example. When growing a single crystal by the temperature gradient method, the high temperature region is preferably 950 ° C. or more, more preferably 1000 ° C. or more. 1000. C force is preferred, more preferred f is 850-950. C. Also, by increasing the growth temperature, for example, silicon carbide single crystals such as 4H—SiC single crystals and 6H—SiC single crystals can be grown at a lower temperature than in the past. Thus, according to the manufacturing method of the present invention, it is possible to produce or grow a silicon carbide single crystal at a lower temperature than in the prior art. In addition, these temperature ranges are examples, and are not limited, for example The heating temperature can be appropriately set according to other conditions.

Next, examples of the present invention will be described. The present invention is not limited to the following examples.

Example 1

This example is an example in which a silicon carbide (SiC) single crystal was manufactured using the crystal growth apparatus shown in FIGS. 1 (A) and (B). The electric furnace 14 used was composed of a resistance heater and heat insulating material. A pressure-resistant and heat-resistant container 13 is arranged in the electric furnace 14, and the pressure-resistant and heat-resistant container 1

A tungsten (W) crucible 15 was placed in 3. A high-purity graphite crucible is placed in the W crucible 15, and metallic lithium (Li) 1 · 2 g (= 0. 1739 mol) and silicon (Si) l. Lg (

= 0.039 mol). Note that carbon (C) as a raw material for the crystal is supplied from the material component of the graphite crucible. The pressure-resistant and heat-resistant container 13 was replaced with an Ar atmosphere, and the atmosphere in the pressure-resistant and heat-resistant container 13 was adjusted together with the pressure by Ar gas supplied from the gas cylinder 11. Next, the temperature in the electric furnace 14 is heated to 850 ° C., and lithium is dissolved to form a flux (melt). Further, in order to dissolve silicon and carbon in the Li flux to supersaturation, hold for 24 hours. did. Thereafter, cooling was continued to 700 ° C. in 72 hours. Thereafter, it was naturally cooled to room temperature to obtain the intended silicon carbide single crystal. The obtained single crystals are shown in FIGS. 2 and 3 (A

) And (B). FIG. 2 is an aggregate of silicon carbide single crystals formed on the side wall of the graphite crucible, and FIGS. 3A and 3B are enlarged views of the obtained silicon carbide single crystal. First, the product in the crucible was taken out and powdered, and X-ray diffraction evaluation was performed on the powder.

. The results are shown in Fig. 4. Fig. 4 is a chart showing the results of the ω / 2 θ scan (rotating the crystal and detector). As shown in the figure, a diffraction peak matching the peak data of 2H_SiC was confirmed, and further, the obtained single crystal was evaluated by X-ray diffraction using a parallel beam method as shown in the schematic diagram of Fig. 5 (A). Did. As shown in the figure, in this evaluation, X-rays are incident from 3.7 degrees, and diffracted light from the single crystal is detected by a detector. A solar slit for extracting only the parallel beam is placed in front of the detector to detect the signal with high resolution. The analysis results are shown in the chart of Fig. 5 (B). Fig. 6 shows peak data with the background of the chart in Fig. 5 (B) removed. As shown in the figure, this evaluation yielded a diffraction peak consistent with the 2H-SiC peak data. These results indicate that the single crystal is It was confirmed to be 2H—SiC single crystal. The X-ray source is not particularly limited. For example, a CuK ct line can be used. Further, the first crystal used for the X-ray patrol is not particularly limited, and for example, InP crystal or Ge crystal can be used.

Example 2

[0028] A silicon carbide single crystal was produced in the same manner as in Example 1 except that the temperature in the electric furnace 14 was heated to 950 ° C and held for 24 hours, and then cooled to 850 ° C in 72 hours. did. The product in the crucible obtained was evaluated for X-ray diffraction in the same manner as in Example 1. The chart in Figure 9 shows the results of this analysis. From this result, the formation of 3C-SiC single crystal was confirmed. Industrial applicability

[0029] As described above, according to the production method of the present invention, a large silicon carbide single crystal can be produced at low cost. Further, according to the production method of the present invention, for example, a large butter-shaped silicon carbide single crystal can be produced at low cost. The silicon carbide single crystal obtained by the production method of the present invention can be preferably used, for example, as a semiconductor device for an in-vehicle power device or an energy device, and its application is not limited and is wide.

Claims

The scope of the claims

[I] Silicon carbide (SiC) single crystal manufacturing method, in which silicon (Si) and carbon (C) are dissolved in an alkali metal flux and reacted to form a silicon carbide single crystal Or a growing production method.

[2] The method according to claim 1, wherein the silicon carbide single crystal is a 2H—SiC single crystal or a 3C—SiC single crystal.

[3] The method according to claim 1, wherein the silicon carbide single crystal is produced or grown by cooling the alkali metal flux that is dissolved when the silicon and the carbon are dissolved.

[4] By heating the silicon, the carbon, and the alkali metal, the silicon and the carbon are dissolved in the alkali metal flux, and the heating state is maintained for a certain time, and then the heating temperature is decreased. The manufacturing method according to claim 3, wherein the alkali metal flux is cooled.

[5] A temperature gradient is formed in the alkali metal flux, the silicon and the carbon are dissolved in a high temperature region of the temperature gradient, and the silicon carbide single crystal is generated in a low temperature region of the temperature gradient. Or the manufacturing method of Claim 1 made to grow.

6. The method according to claim 1, wherein the alkali metal power is at least one selected from the group consisting of lithium (Li), sodium (Na) and potassium (K).

7. The production method according to claim 1, wherein the alkali metal is lithium (Li).

[8] The production method according to claim 1, wherein the alkali metal flux further contains an alkaline earth metal.

[9] The production method according to claim 1, wherein the reaction is performed in a reaction vessel, and the carbon is supplied from material components of the reaction vessel.

[10] The production method according to claim 9, wherein the reaction vessel is a vessel formed of a carbon-based material.

[II] The production method according to claim 10, wherein the carbonaceous material is graphite.

12. The production method according to claim 1, wherein a silicon carbide crystal prepared in advance is used as a seed crystal, and a new silicon carbide single crystal is grown using the seed crystal as a nucleus.

[13] The production method according to claim 1, wherein the silicon carbide single crystal is produced or grown under a pressurized atmosphere.

[14] The production method according to claim 1, wherein the silicon carbide single crystal is produced or grown in an inert gas atmosphere.

[15] The production method according to claim 14, wherein the inert gas is at least one of argon (Ar) gas and hydrocarbon gas.

16. The production method according to claim 15, wherein the hydrocarbon gas is at least one of methane gas and propane gas.

17. The manufacturing method according to claim 1, wherein the alkali metal flux further contains a doping impurity.

[18] A silicon carbide single crystal obtained by the production method according to claim 1, which is a silicon carbide (SiC) single crystal.

[19] The silicon carbide single crystal according to claim 18, which is a 2H—SiC single crystal or a 3C—SiC single crystal.

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